IN PRESS: MEMORY & COGNITION Why Does Working Memory Span Predict Complex Cognition? Testing the Strategy-Affordance Hypothesis

We introduce and empirically evaluate the strategy-affordance hypothesis, which holds that individual differences in strategy use will mediate the relationship between performance on a working memory (WM) span task and another cognitive task only when the same strategies are afforded by both tasks. One-hundred and forty eight participants completed basic memory tasks and verbal span tasks that afford the same strategies, such as imagery and sentence generation, and completed reading comprehension tasks that afford different ones, such as self-questioning and summarization. Effective strategy use on WM span tasks accounted for variance in the spanmemory relationship, but not for the span-comprehension relationship, supporting the strategyaffordance hypothesis. Strategy use only mediated the span-cognition relationship when both tasks afforded the same strategies. Strategy Affordance Hypothesis 3 Widespread interest in working memory (WM) span tasks is driven largely by their success in predicting other cognitive abilities, such as reasoning, memory, and comprehension (e.g., Ackerman, Beier, & Boyle, 2005; Kane, Hambrick, & Conway, 2005). These spancognition correlations presumably arise because span tasks measure a domain-general construct, which in turn, is partly responsible for performance on a variety of cognitive tasks. Span tasks may tap executive attention (Engle & Kane, 2004), mental binding (Oberauer, 2005), processing speed (Salthouse, 1991), attentional inhibition (Hasher, Lustig, & Zacks, 2007), or other processes (for reviews, see Conway, Jarrold, Kane, Miyake, & Towse, 2007), which may contribute to performance on memory, reasoning, comprehension, and other tasks. Recently, researchers have explored (a) the degree to which variation in strategy use predicts individual differences in span performance and (b) the degree to which variation in strategy use may account for span-cognition relationships. Concerning the former issue, individual differences in strategy use do account for significant variance on span performance (Dunlosky & Kane, 2007; Engle, Cantor, & Carullo, 1992; Friedman & Miyake, 2004; Kaakinen & Hyona, in press; McNamara & Scott, 2001; Turley-Ames & Whitfield, 2003). That is, span performance is higher when individuals report using normatively effective strategies (e.g., interactive imagery or sentence generation) than when they report using less effective ones (e.g., reading). Although strategy use can influence span performance, effective strategy use does not appear to account for span-cognition relationships (Dunlosky & Kane, 2007; Engle et al., 1992; Friedman & Miyake, 2004; Turley-Ames & Whitfield, 2003). For example, Turley-Ames and Whitfield (2003) examined whether individual differences in strategy use mediated the relationship between performance on the operation span (OSPAN) task and the Nelson-Denny reading test. They found that the use of normatively effective strategies on the OSPAN task did Strategy Affordance Hypothesis 4 not predict performance on the Nelson-Denny reading test. Such evidence is inconsistent with a general strategy-mediation hypothesis (cf. McNamara & Scott, 2001), which is that individual differences in effective strategy use entirely (or substantially) mediate the relationship between span performance and all criterion tasks. In the present research, we evaluate another version of strategy-mediation hypotheses, which predicts that strategy use on span tasks will mediate the span-cognition relationship for some tasks but not others. According to this strategy-affordance hypothesis, strategy use will mediate span-cognition relationships only when the same strategies are afforded by both tasks. For instance, because the to-be-remembered stimuli for the OSPAN task are individual words, they afford several associative strategies, such as rehearsal, imagery, and sentence generation (Dunlosky & Kane, 2007; Kaakinen & Hyona, in press; McNamara & Scott, 2001; Turley-Ames & Whitfield, 2003). Individual differences in strategy use should therefore mediate a spancognition relationship when the cognitive task also affords the use of these effective strategies, such as paired-associate learning (Richardson, 1998) or learning lists of words for free recall (Hertzog, McGuire, & Lineweaver, 1998). By contrast, the strategies afforded by the OSPAN task cannot be readily used to improve performance on many criterion tasks typically used in the field. Consider again the results from Turley-Ames and Whitfield (2003), who used the Nelson-Denny test as a measure of reading ability. In this task, participants read several passages and then answer multiple-choice questions about them. Although strategies such as self-questioning and summarization can be used on this task (Rich & Shepherd, 1993), these strategies are not afforded by span tasks. Thus, the strategyaffordance hypothesis predicts that strategy use will not mediate the relationship between performance on the span task and the Nelson-Denny test. Strategy Affordance Hypothesis 5 To date, no evidence is available that evaluates conditions in which strategies are expected to mediate span-cognition relationships, because previous experiments have used criterion tasks that do not afford the associative strategies afforded by verbal span tasks. In particular, criterion tasks have measured general verbal knowledge (i.e., verbal analogies in Dunlosky & Kane, 2007; verbal scholastic assessment test [SAT] in Engle et al., 1992) and reading comprehension (i.e., SAT reading comprehension in Friedman & Miyake, 2004; NelsonDenny test in Turley-Ames & Whitfield, 2003). A major aim of the current study was to empirically evaluate the strategy-affordance hypothesis by examining whether strategy use more strongly mediates span-cognition relationships when the cognitive tasks afford the same strategies than when they do not. To evaluate the strategy-affordance hypothesis, we assessed strategy production on various cognitive tasks. For span tasks, we used the OSPAN and reading span (RSPAN) tasks. Strategy production on both span tasks was measured through set-by-set strategy reports. These strategy reports consisted of a prompt asking the participants whether they used, on a given trial, either reading, repetition, sentence generation, mental imagery, meaningful grouping, or a different strategy to remember the target items. These options were chosen because prior research indicated that people use them on verbal span tasks (Dunlosky & Kane, 2007; TurleyAmes & Whitfield, 2003). Strategies were categorized into normatively effective ones (imagery, sentence generation, and grouping) and less effective ones (e.g., reading and repetition) because previous research has demonstrated that memory performance is typically higher for the normatively effective strategies on episodic memory tasks (for reviews, see Hertzog et al., 1998; Richardson, 1998) and on the OSPAN task (Dunlosky & Kane, 2007). Strategy Affordance Hypothesis 6 The validity of these set-by-set strategy reports has been established by demonstrating significantly higher performance on trials in which participants reported using normatively effective strategies as compared to trials in which they reported using less effective strategies on the OSPAN and RSPAN tasks (e.g., Dunlosky & Kane, 2007; Bailey, Dunlosky, & Hertzog, 2008). Making these strategy reports appears to have minimal reactive effects on task performance and on strategy use (Dunlosky & Kane, 2007), partly because people use these strategies even when they are not required to report strategies while performing these tasks (McNamara & Scott, 2001). Moreover, Dunlosky and Kane (2007) used both concurrent (completed immediately after recall of each set) and retrospective (completed after all sets had been completed) set-by-set strategy reports. They found high consistency between both types of reports, suggesting minimal forgetting of the strategies that were used during the OSPAN task when they were reported after the task was completed. Because the reports yield similar results, we collected only retrospective strategy reports. For the criterion tasks, we selected free-recall and paired-associate recall tasks because they afford the same effective strategies as these span tasks (e.g., Hertzog et al., 1998; Richardson, 1998). On the free-recall task, effective strategy production was measured through global strategy reports, in which participants described any strategy they used to remember the words. Strategy production was assessed on the paired-associate recall task via retrospective item-by-item reports. We also selected the Nelson-Denny test and SAT practice questions because they are commonly-used criterion tasks that afford different strategies than do verbal span tasks (Rich & Shepherd, 1993). Strategy production on both reading comprehension tasks was measured through global strategy reports, in which participants explained any strategies they used to complete the tasks. Strategy Affordance Hypothesis 7 The strategy-affordance hypothesis predicts that individual differences in the proportion of normatively effective strategy use will mediate (or partially mediate) the correlation between span and memory tasks but not between span and reading comprehension tasks. Method Participants A total of 148 undergraduates (86 women) from introductory psychology courses at Kent State University participated to complete a course requirement. Their mean age was 19.3 years. Materials OSPAN task. We used the version of the OSPAN task described in Kane et al. (2004). Participants saw a mathematical operation and a to-be-remembered word (e.g., “Is (3 x 2) + 5 = 10? phone”). They read the equation aloud, reported whether it was correct, and then read the word aloud. Immediately thereafter, the next operation-word pair appeared on-screen. A recall cue followed the final pair of the trial, and participants wrote the target words in serial order. The OSPAN task consisted of 15 experimenter-paced trials that ranged from three to seven operationword pairs. The order of set sizes was initially randomized and that order was used for all participants. Following the final trial, participants completed retrospective set-by-set strategy reports created by Dunlosky and Kane (2007). The stimuli from each trial were re-presented together on-screen (including all of the equations and words) and participants indicated which strategy they used to remember the words on that particular trial. RSPAN task. We used a modified version of the RSPAN task from Kane et al. (2004). Participants saw either a logical or nonsensical sentence and an unrelated word (e.g., “Mr. Owens left the lawnmower in the lemon.? eagle”). Participants read the sentence aloud, reported whether it made sense, and then read the word aloud. Once the word was read aloud, the next Strategy Affordance Hypothesis 8 sentence-word pair appeared on-screen. After the final pair of each trial, a recall cue prompted participants to write the target words in serial order. The RSPAN task consisted of 15 experimenter-paced trials that ranged from three to seven sentence-word pairs presented in random order. The same set-by-set strategy reports from the OSPAN task were administered after the final trial of the RSPAN task. Performance on both span tasks was computed using partial-credit unit scoring (see Conway, Kane, Bunting, Hambrick, Wilhelm, & Engle, 2005). Paired-associates cued-recall task. Participants studied 40 unrelated word pairs (e.g., DOCTOR – LOBSTER) presented on the computer screen at a 5-second rate. During the recall phase, the cues (e.g., DOCTOR) were presented in the same order as during encoding, and participants typed in the correct response (e.g., LOBSTER). Following the final recall trial, participants completed a strategy report in which they recounted which specific strategy (passive reading, rote repetition, interactive imagery, sentence generation, or “other”) they had used to remember each word pair (re-presented on-screen). Free recall. A list of 20 words appeared individually on-screen at a 5-second rate. Participants immediately recalled the words in any order. After recall, participants described the strategies they used to help them remember the words and they could indicate using more than one strategy. We computed the percentage of participants that reported any given strategy. Nelson-Denny reading comprehension test. Participants read 8 passages and answered multiple-choice questions after each, with a 12 minute time limit. Scores reflected the proportion of correctly answered items. After they completed the Nelson-Denny test, participants completed a global strategy report in which they described any strategy used to help them complete the task. The percentage of participants that reported any given strategy was computed. Strategy Affordance Hypothesis 9 Scholastic Assessment Test (SAT) practice questions. Participants read 8 expository passages and answered 8 questions about each, with a 15 min time limit (from Rawson & Dunlosky, 2002). Scores reflected the proportion of correctly answered items. After finishing this task, participants completed a global strategy report in which they described any strategy used to help them complete the task. The percentage of participants that reported any given strategy was computed. Procedure Participants completed two 1-hour sessions, separated by one week. Each session consisted of one WM span task, one reading comprehension task, and one memory task, with the tasks administered on a Dell Optiplex GX280 computer. In session 1, participants completed the the OSPAN task, Nelson-Denny test, and the paired-associates task. In session 2, they completed the RSPAN task, SAT practice questions, then the free-recall task. Results Before we present the mediation analyses most relevant to the strategy-affordance hypothesis, we present (a) self-reported strategy use to establish that participants employed normatively effective strategies while performing the span tasks and (b) span performance as a function of strategy use to validate that effective strategies improved span performance. These analyses replicate Dunlosky and Kane (2007) who investigated only the OSPAN task, but importantly, they also extend the results to the RSPAN task. Proportion of Reported Strategy Use For any given task, few participants reported using every strategy. To increase the power of analyses, we divided responses on the strategy reports into two categories: normatively effective and normatively less effective. Given outcomes from prior research (e.g., Richardson, Strategy Affordance Hypothesis 1